The use of microwave energy to heat and cook comestibles has been an unqualified commercial success. Today, it is very hard to find an American home without a microwave oven.
As commonplace as the microwave oven has become, however, it is exceptionally surprising to observe the paucity of such heating devices for other household and industrial uses.
For example, as early as 1969, a method and apparatus was suggested for drying and sterilizing fabrics, as illustrated in U.S. Pat. No. 3,605,272, issued: Sept. 20, 1971.
The drying of wet fabrics should have become a commercial reality after fifteen years of research.
One of the drawbacks of perfecting a microwave clothes dryer has been the power requirements. Unlike a microwave oven, which requires a magnetron that generates 400 to 800 watts of microwave power, a typical clothes dryer needs a magnetron generating in excess of two kilowatts. A single magnetron generating this amount of power is very expensive.
Another possible problem with suggested microwave clothes dryer designs, is the inability to transfer and/or distribute the generated power uniformly to the wet fabric. Often hot spots develop in the fabric mass. Such hot spots can cause scorching of the fabric, and are a fire safety concern.
To the best of our knowledge, it never has been suggested that more than one magnetron be utilized to improve heating uniformity. Using two or more magnetrons would solve the first aforementioned problem, wherein several low cost magnetrons could efficiently replace one expensive unit.
However, a clothes dryer with two or more magnetrons would not necessarily be more efficient in the transfer or distribution of the microwave energies. Magnetrons whose generated waves share the same plane of propagation will interfere with each other. Also, unabsorbed power that reflects off the heating chamber walls can enter the wave guide of an adjacent magnetron through its antenna and alter its operation and efficiency.